The present invention relates to a molded tooling fixture for use in a process for electrochemically stripping coatings from turbine engine airfoils.
Gas turbine engines in aircraft are taken out of service at periodic intervals and regular maintenance service is performed on them. Part of the regular repair sequence for the blades and vanes (individually or collectively referred to hereafter as xe2x80x9cairfoilsxe2x80x9d) of these engines includes the removal and then replacement of the worn coatings from their surfaces. These coatings are usually either an aluminide coating or an MCrAlY coating. The underlying base metal of the airfoils is generally made of either a nickel base alloy or a cobalt base alloy. These coatings provide the airfoils with a thermal barrier to the hot corrosive environment in which these airfoils operate.
In the past, these aluminide and MCrAlY coatings were removed from airfoils by soaking the airfoils either in nitric acid solutions or in hydrochloric acid solutions in high concentrations for up to six hours at elevated temperatures. The soaking process however is disadvantageous in several respects. It is extremely labor intensive and can produce non-uniform and unpredictable results. It can also damage or destroy airfoils if improperly carried out. Furthermore, each airfoil requires extensive masking to protect areas sensitive to the acid soaking solution. Such areas include internal surfaces and the root section of the airfoil. These masking operations are costly, add significant time to the repair process and, if not properly carried out, can lead to damaged or destroyed parts. Still further, these soaking processes may result in extensive amounts of acidic waste solution that must be properly disposed of as well as have a long cycle time and require relatively large amounts of energy to heat the acidic solutions.
A process for electrochemically stripping a coating from an airfoil is described in U.S. Pat. No. 6,176,999 to Jaworowski et al., which is hereby incorporated by reference herein. In this process, an airfoil to be stripped is immersed in an electrochemical acid bath for a sufficient period of time to remove the coating from the airfoil while the airfoil in the electrochemical acid bath is maintained with a controlled absolute electrical potential with respect to a reference electrode. Prior to being immersed in the bath, the airfoil is masked to cover any acid sensitive surfaces. The airfoil parts are affixed to an insulating fixture at the root section of the airfoil. The insulating fixture is made of titanium or another noble metal material.
Despite the advancements in electrochemical stripping of airfoils, there remains a need for tooling fixtures which protect the root section and adjacent serrations of an airfoil from etching damage.
Accordingly, it is an object of the present invention to provide a tooling fixture which protects the root section and adjacent serrations during an electrochemical stripping operation.
It is a further object of the present invention to provide a tooling fixture as above which is easily installed and which achieves better stripping results.
The foregoing objects are attained by the tooling fixture of the present invention.
In accordance with the present invention, a tooling fixture for supporting an airfoil during an electrochemical stripping process broadly comprises a holder for receiving the airfoil, which holder has a first slot in which a serrated portion of the airfoil is positioned. The holder is formed from an electrically non-conductive material such as molded plastic. The first slot has at least one serrated surface which mates with at least one serration on the airfoil. The fixture further includes a support arm on which the holder is supported. The support arm is also formed from an electrically non-conductive material such as molded plastic. Still further, the fixture includes a rod formed from an electrically conductive material which sits in a groove in the support arm and which contacts a lower surface of the airfoil.
Other details of the tooling fixture of the present invention, as well as other objects and advantages attendant thereto, are set forth in the following detailed description and the accompanying drawings wherein like reference numerals depict like elements.